Recently, in an antifouling paint and other areas, public attentions are directed to the use of resinous filler particles which can be hydrolyzed in an ionic atmosphere as in sea water of weak alkaline condition and gradually decomposed and dissolved out. They are specifically useful for prolonging antifouling and polishing effects of an antifouling paint and attaining energy saving and others therewith.
Various resins have been proposed for this end as, for example, acrylic resins with halogenated aliphatic acid bonding units or electron attractive group containing acyl bondings (e.g. Japanese Patent Appln. No. 101463/81 and ibid 198240/81); acrylic resins containing organic tin salts (e.g. Japanese Patent Appln. Kokai No. 98570/82); and polyester resins having metal ester bondings in the polymer main chain (e.g. Japanese Patent Appln. No. 165921/81 and ibid 165922/81) and the like.
However, they were merely developed as resinous vehicles for antifouling paints, requiring film-forming properties and optimum film performance and therefore, there were in fact various limitations on the employable resins in respect of molecular weight, metal contents and the like, besides the hydrolysis natures thereof.
In a coating composition area, attempts have also been made to add, to a film-forming resinous varnish, resin powders for the improvement in application characteristics, without increasing viscosity, of the coating composition. Therefore, even in an antifouling paint, hydrolysis type resin powders having no film-forming properties have been actually examined. For example, in Japanese Patent Publication No. 3830/86, are disclosed film-forming polymer compositions comprising a polyacrylic acid salt having a basic unit of the formula: ##STR1## in which M stands for Cu or Zn.
It is stated that said polyacrylic acid salts may be of film-forming type or of non-film-forming type and the molecular weight is in a range of 5000 to 1.times.10.sup.6. Therefore, it is clear that hydrolysis type crosslinked resins having no film-forming properties are likewise suggested in this publication. However, in preparing said resins, a specific method is used, wherein a carboxyl bearing acrylic resin is first neutralized with caustic soda and dissolved in an aqueous medium and thus obtained polymer solution is reacted with a metal salt, thereby forming precipitation of insoluble polyacrylic acid salt. In this type of reaction, the soluble resin is gradually changed to insoluble type with the progress of ion-exchange reaction, and the formed insoluble resins are precipitated as amorphous masses each varying in size and shape. Since a smaller precipitate has a larger surface area and more rapidly hydrolyzed with sea water than a larger one, when the aforesaid precipitates are used in a self-polishing type antifouling paint, smaller precipitates are quickly hydrolyzed and consumed and larger precipitates are wastefully let out the coating with the dissolved resin. Therefore, indeed an effective antifouling can be expected with the composition in an early stage, but a long-lasting effect cannot be obtained therewith. Furthermore, in the method of said Japanese Patent Publication No. 830/86, an acrylic resin and a metal salt are reacted with each other each in solution form in water, and loss in solubility of the resin is the only cause of said precipitation. Since the reaction makes steady progress at the surface of precipitated resin interacted with aqueous metal salt solution, the metal ester bondings are always present in a higher concentration at the surface layers of the precipitates. Moreover, the precipitated resins do necessarily have a number of acid groups together with metal ester bondings, because precipitation is occurred in an aqueous medium by the decrease in solubility of the resin. They are, therefore, too hygroscopic to use as the resinous filler in a polishing type antifouling paint. For these reasons, a long-lasting antifouling effect cannot be expected with the coating composition added with the disclosed precipitates.
Since the precipitates are not of spherical form, they can never be maintained in a stabilized state of dispersion in a coating composition.
It is, therefore, an object of the invention to provide disintegration type, crosslinked acrylic resin particles which can be added as resinous filler in an antifouling paint, and thoroughly disintegrated from the interior and exterior of the respective grain, in an ionic atmosphere. An additional object of the invention is to provide the acrylic resin particles with the aforesaid characteristic properties, prepared by a method which is simple but still effective for the control of water susceptibility and hydrolysis rate of the formed resin particles.
Further object of the invention is to provide disintegration type, spherical, internally crosslinked acrylic resin particles which are particularly useful in a polishing type antifouling paint. Other objects of the invention shall be clear from the description of the specification and accompanied claims.